sagenb -- add "how to test" directions to the sagenb README.txt

[was]

1. Doctest: 
       sage -t -sagenb 
2. Run the Selenium test suite:
       sage -python sagenb/testing/run_tests.py 

To use Selenium, you must visit http://seleniumhq.org/download/ and:

      * Download and extract Selenium RC ("the Selenium Remote Control")

      * Run it as follows on Linux:
             $ cd /path/to/selenium-remote-control-1.0.3/selenium-server-1.0.3
             $ java -jar selenium-server.jar
             $ cd /path/to/sagenb-0.8/src/sagenb
             $ sage  -python sagenb/testing/run_tests.py

      * Run it as follows on OS X:
             $ cd /path/to/selenium-remote-control-1.0.3/selenium-server-1.0.3
             $ cd /path/to/sagenb-0.8/src/sagenb
             $ sage
             sage: import sagenb.testing.run_tests as rt 
             sage: rt.setup_tests('localhost', False, '*firefox')
             sage: rt.run_any()

That the instructions for OS X are different is probably a bug.

[acleone]

Added a development section. Replaces the last patch

[acleone]

Newest Version. Added a "Reviewing Patches" section. Apply only this.

[mpatel]

Should someone review the latest patch? I noticed two minor problems:

• dwnload
• An extra * in b) * Run it as follows:

Also, should the reviewing section first refer in some way to steps 1,2,3, and/or 6 of the development section?